Matrilysin is a metalloprotease possessing activity against a broad range of matrix substrates including laminin, fibronectin, elastin and proteoglycans. We have identified mononuclear phagocytes as the first normal human cell source of this enzyme. To expand our understanding of matrilysin expression, three specific aims are proposed. 1) To define the role of differentiation on matrilysin synthesis, cells spanning the spectrum from hematopoietic progenitors to fully differentiated tissue macrophages will be studied by immunoprecipitation with specific polyclonal antiserum and in situ hybridization to matrilysin cRNA. 2) Regulation of matrilysin synthesis will be examined in both normal and transformed monocytic cells. Steady-state mRNA levels of cells exposed to LPS will be assessed by Northern hybridization. Nuclear run-ons and message decay analysis will be performed to evaluate pre-translational control mechanisms. Established modulators of other metalloproteases will also be investigated for ability to regulate matrilysin synthesis. 3) To gain insights into the biological role of matrilysin, mononuclear phagocytes in pathological conditions will be studied. The effects of lipid-loading on matrilysin synthesis will be examined in vitro and correlated with matrilysin expression in atherosclerotic plaques, as detected by in situ hybridization. In situ hybridizations will also be performed on tissue samples of disease states characterized by connective tissue degradation. It is hoped that these studies will further our understanding of the human mononuclear phagocyte's role in extracellular matrix remodeling.